The iridium oxide (IrO ₂ ) catalyst for the oxygen evolution reaction used industrially (in proton exchange membrane water electrolyzers) is scarce and costly. Although ruthenium oxide (RuO ₂ ) is a promising alternative, its poor stability has hindered practical application. We used well-defined extended surface models to identify that RuO ₂ undergoes structure-dependent corrosion that causes Ru dissolution. Tantalum (Ta) doping effectively stabilized RuO ₂ against such corrosion and enhanced the intrinsic activity of RuO ₂ . In an industrial demonstration, Ta-RuO ₂ electrocatalyst exhibited stability near that of IrO ₂ and had a performance decay rate of ~14 microvolts per hour in a 2800-hour test. At current densities of 1 ampere per square centimeter, it had an overpotential 330 millivolts less than that of IrO ₂ .

Rechargeable magnesium batteries are poised to be viable candidates for large-scale energy storage devices in smart grid communities and electric vehicles. However, the energy density of previously proposed rechargeable magnesium batteries is low, limited mainly by the cathode materials. Here, we present new design approaches for the cathode in order to realize a high-energy-density rechargeable magnesium battery system. Ion-exchanged MgFeSiO₄ demonstrates a high reversible capacity exceeding 300 mAh·g⁻¹ at a voltage of approximately 2.4 V vs. Mg. Further, the electronic and crystal structure of ion-exchanged MgFeSiO₄ changes during the charging and discharging processes, which demonstrates the (de)insertion of magnesium in the host structure. The combination of ion-exchanged MgFeSiO₄ with a magnesium bis(trifluoromethylsulfonyl)imide–triglyme electrolyte system proposed in this work provides a low-cost and practical rechargeable magnesium battery with high energy density, free from corrosion and safety problems.

We investigated the reversible charge compensation mechanism of an Li ₂ MnO ₃ electrode using soft XAS analysis. We concluded that both the Mn and O ions participated in the charge compensation reactions during the reversible redox cycles.